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  <text>Original link: &lt;a href="http://blog.stevex.net/index.php/string-formatting-in-csharp/"&gt;http://blog.stevex.net/index.php/string-formatting-in-csharp/&lt;/a&gt;

&lt;strong&gt;String Formatting in C#
&lt;/strong&gt;
I couldnâ€™t find a quick reference to .NET string formatting using the String.Format() function, so I created this one.

When I started working with the .NET framework, one thing puzzled me. I couldnâ€™t find sprintf(). sprintf() is the C function that takes an output buffer, a format string, and any number of arguments, and builds a string for you. For example:

&lt;code&gt;    char szError[256];
    sprintf(szError, â€œError %d occurred.\nâ€?, nError);&lt;/code&gt;

This would write â€œError 12 occurred.â€? into the szError buffer (assuming nError was 12). Itâ€™s a basic part of C programming and most C++ programmers still use it though better functionality is available in the STL because sprintf is simple to use and clear. The STL equivalent would be:

&lt;code&gt;    str &lt; &lt; â€œError â€? &lt;&lt; nError &lt;&lt; â€? occurred.â€? &lt;&lt; endl;&lt;/code&gt;

Or something close to that. Itâ€™s type-safe, and more OO than sprintf, but not as easy to read and not as easy to localize.

The .NET framework handles strings very nicely - but it takes some getting used to. The rough equivalent of sprintf in .NET is the static String.Format function, which takes a format string and some arguments, and generates an output string. (This is a nice improvement over sprintf since thereâ€™s no chance youâ€™ll overflow the output buffer). For example:

&lt;/code&gt;&lt;code&gt;    string errorString = String.Format(â€?Error {0} occurred.â€?, nError);&lt;/code&gt;

Teeming with metadata, the .NET environment doesnâ€™t need the format string to say what type of data youâ€™re formatting, just where you want it. (A common sprintf bug is supplying the wrong data type - thereâ€™s no protection from using %s instead of %d and having your program crash when sprintf is called).

The {0} in the string above is replaced with the value of nError, but what if you want to specify the number of digits to use? Or the base (hexadecimal etc)? The framework supports all this, but where it seemed confusing is that itâ€™s not the String.Format function that does the string formatting, but rather the types themselves.

Every object has a method called ToString that returns a string representation of the object. The ToString method can accept a string parameter, which tells the object how to format itself - in the String.Format call, the formatting string is passed after the position, for example, â€œ{0:##}â€?

The text inside the curly braces is {index[,alignment][:formatString]}. If alignment is positive, the text is right-aligned in a field the given number of spaces; if itâ€™s negative, itâ€™s left-aligned.

&lt;strong&gt;Strings
&lt;/strong&gt;

There really isnâ€™t any formatting within a strong, beyond itâ€™s alignment. Alignment works for any argument being printed in a String.Format call.

&lt;code&gt;String.Format(â€?-&gt;{1,10}&lt; -â€?, â€œHelloâ€?); 	-&gt; Hello&lt; -
String.Format(â€?-&gt;{1,-10}&lt; -â€?, â€œHelloâ€?); 	-&gt;Hello &lt; -&lt;/code&gt;

&lt;strong&gt;Numbers&lt;/strong&gt;

Basic number formatting specifiers:

&lt;/code&gt;&lt;code&gt;Specifier 	Type 	Format 	Output (Passed Double 1.42) 	Output (Passed Int -12400)
c 	Currency 	{0:c} 	$1.42 	-$12,400
d 	Decimal (Whole number) 	{0:d} 	System.FormatException 	-12400
e 	Scientific 	{0:e} 	1.420000e+000 	-1.240000e+004
f 	Fixed point 	{0:f} 	1.42 	-12400.00
g 	General 	{0:g} 	1.42 	-12400
n 	Number with commas for thousands 	{0:n} 	1.42 	-12,400
r 	Round trippable 	{0:r} 	1.42 	System.FormatException
x 	Hexadecimal 	{0:x4} 	System.FormatException 	cf90&lt;/code&gt;

Custom number formatting:

&lt;code&gt;Specifier 	Type 	Example 	Output (Passed Double 1500.42) 	Note
0 	Zero placeholder 	{0:00.0000} 	1500.4200 	Pads with zeroes.
# 	Digit placeholder 	{0:(#).##} 	(1500).42 	
. 	Decimal point 	{0:0.0} 	1500.4 	
, 	Thousand separator 	{0:0,0} 	1,500 	Must be between two zeroes.
,. 	Number scaling 	{0:0,.} 	2 	Comma adjacent to Period scales by 1000.
% 	Percent 	{0:0%} 	150042% 	Multiplies by 100, adds % sign.
e 	Exponent placeholder 	{0:00e+0} 	15e+2 	Many exponent formats available.
; 	Group separator 	see below 		&lt;/code&gt;

The group separator is especially useful for formatting currency values which require that negative values be enclosed in parentheses. This currency formatting example at the bottom of this document makes it obvious:

&lt;strong&gt;Dates&lt;/strong&gt;

Note that date formatting is especially dependant on the systemâ€™s regional settings; the example strings here are from my local locale.

&lt;code&gt;Specifier 	Type 	Example (Passed System.DateTime.Now)
d 	Short date 	10/12/2002
D 	Long date 	December 10, 2002
t 	Short time 	10:11 PM
T 	Long time 	10:11:29 PM
f 	Full date &amp; time 	December 10, 2002 10:11 PM
F 	Full date &amp; time (long) 	December 10, 2002 10:11:29 PM
g 	Default date &amp; time 	10/12/2002 10:11 PM
G 	Default date &amp; time (long) 	10/12/2002 10:11:29 PM
M 	Month day pattern 	December 10
r 	RFC1123 date string 	Tue, 10 Dec 2002 22:11:29 GMT
s 	Sortable date string 	2002-12-10T22:11:29
u 	Universal sortable, local time 	2002-12-10 22:13:50Z
U 	Universal sortable, GMT 	December 11, 2002 3:13:50 AM
Y 	Year month pattern 	December, 2002
&lt;/code&gt;

The â€˜Uâ€™ specifier seems broken; that string certainly isnâ€™t sortable.

Custom date formatting:

&lt;code&gt;Specifier 	Type 	Example 	Example Output
dd 	Day 	{0:dd} 	10
ddd 	Day name 	{0:ddd} 	Tue
dddd 	Full day name 	{0:dddd} 	Tuesday
f, ff, â€¦ 	Second fractions 	{0:fff} 	932
gg, â€¦ 	Era 	{0:gg} 	A.D.
hh 	2 digit hour 	{0:hh} 	10
HH 	2 digit hour, 24hr format 	{0:HH} 	22
mm 	Minute 00-59 	{0:mm} 	38
MM 	Month 01-12 	{0:MM} 	12
MMM 	Month abbreviation 	{0:MMM} 	Dec
MMMM 	Full month name 	{0:MMMM} 	December
ss 	Seconds 00-59 	{0:ss} 	46
tt 	AM or PM 	{0:tt} 	PM
yy 	Year, 2 digits 	{0:yy} 	02
yyyy 	Year 	{0:yyyy} 	2002
zz 	Timezone offset, 2 digits 	{0:zz} 	-05
zzz 	Full timezone offset 	{0:zzz} 	-05:00
: 	Separator 	{0:hh:mm:ss} 	10:43:20
/ 	Separator 	{0:dd/MM/yyyy} 	10/12/2002&lt;/code&gt;

Enumerations

&lt;code&gt;Specifier 	Type
g 	Default (Flag names if available, otherwise decimal)
f 	Flags always
d 	Integer always
x 	Eight digit hex.&lt;/code&gt;

Some Useful Examples

&lt;code&gt;String.Format(â€?{0:$#,##0.00;($#,##0.00);Zero}â€?, value);
&lt;/code&gt;

 This will output â€œ$1,240.00â€³ if passed 1243.50. It will output the same format but in parentheses if the number is negative, and will output the string â€œZeroâ€? if the number is zero.

&lt;code&gt;String.Format(â€?{0:(###) ###-####}â€?, 8005551212);&lt;/code&gt;

    This will output â€œ(800) 555-1212â€³.

If you have any questions about string formatting, or pretty much anything related, drop by the Forum and ask it there. Itâ€™s an easier place to talk than in the comments section here.
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  <last_update>2007-10-04T00:52:37.1430806Z</last_update>
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